Food Chemistry and Major Constituents

Food Chemistry

• Food chemistry studies chemical processes and interactions within food.
• It analyzes the composition, structure, and properties of foods.
• Examines chemical changes during processing and consumption.
• Addresses the chemistry of water, carbohydrates, proteins, lipids, vitamins, minerals, and enzymes.

Major Food Constituents

• Food contains major constituents: carbohydrates, fats, and proteins.
• Minor constituents: vitamins, minerals, enzymes, pigments, flavors, acids, and water.

Food Classification by Function

• Energy Yielding Foods (EYF): Rich in carbohydrates and fats.
  • 1 gram of carbohydrate provides 4 kilocalories.
  • 1 gram of fat provides 9 kilocalories.
• Body Building Foods (BBF): Rich in proteins.
  • Milk, meat, eggs, and fish are good sources of high biological value proteins.
• Protective Foods (PF): Rich in vitamins, minerals, and proteins.
  • Two categories:
    • Foods high in vitamins, minerals, and proteins (milk, eggs, fish, liver).
    • Foods rich in vitamins and minerals (green leafy vegetables and some fruits).

Water in Food

• Water is an essential food component.
• It exists as an intracellular or extracellular component in plant and animal products.
• Water acts as a dispersing medium and solvent.
• The presence of water in food:
  • Moisture content: Amount of water present.
  • Water activity (aw): The form in which water exists.

Forms of Water in Food

• Free water: Most abundant form, easily removed by drying.
  • Acts as a dispersing agent and solvent.
• Absorbed water: Attached to the surface of molecules like polysaccharides and proteins.
  • Not easily squeezed out.
• Bound water: Tightly bound to macromolecules or organelles.
  • Unavailable for microbial activity or quality degradation.
  • Freezes at very low temperatures.

Water Activity (aw)

• Water activity is the measure of available water for microbial, enzymatic, or chemical reactions.
• It represents the amount of free water in a sample.
• Influences the shelf life of food.
• Each microorganism has a critical aw below which it cannot grow.

Water Activity and Food Preservation

• Lowering aw retards microbial growth, enzyme activity, and non-enzymatic browning.
• Additives with high water binding capacity (humectants) are used to decrease aw, including common salts, glycerol, and sucrose.

Calculating Water Activity

• aw is the ratio of water vapor pressure of a substance to the vapor pressure of pure water at the same temperature.
• aw = P / P0
  • P: vapor pressure of water in the substance.
  • P0: vapor pressure of pure water.
• Bound water is inversely related to water activity.
• Pure distilled water has an aw of 1.0.
• Temperature influences vapor pressure.

Water Activity Meter (Manometer)

• Used to measure aw.

Relative Humidity and Water Activity

• Relative humidity (RH) is the percentage of water vapor in the air.
• aw is a fraction, so RH = aw x 100.
• Equilibrium relative humidity (ERH): RH at which the food neither gains nor loses moisture.

Microbial Growth and Water Activity

• Microbial growth is directly linked to aw.
• Water migrates from high aw to low aw areas.
• Different microorganisms have different aw requirements for growth.
• Higher aw typically supports more microorganisms.
• Bacteria generally require aw ≥ 0.91, fungi ≥ 0.6.

Moisture Content vs. Water Activity

• Moisture content: The amount of water in a product.
• Water Activity: A measure of available water for microbial growth.

Water Activity and Food Shelf Life

• Water activity is a critical factor in food product design and safety.
• Maintaining a low aw can inhibit mold growth and extend shelf life.
• Water activity is used as a critical control point in Hazard Analysis and Critical Control Points (HACCP) programs.

Dehydration and Food Preservation

• Dehydration is a traditional method of food preservation.
• Removing water reduces aw, making it unavailable for microbial growth.
• Dry foods are more stable than wet foods due to low aw.
• Drying prevents the growth of food poisoning bacteria.
• Osmophilic yeasts and some molds can grow at aw between 0.6 to 0.65.